Topics: AIX, System Admin

Resizing the jfs log

In general IBM recommends that JFS log devices be set to 2MB for every 1GB of data to be protected. The default jfslog for rootvg is /dev/hd8 and is by default 1 PP large. In some cases, file system activity is too heavy or too frequent for the log device. When this occurs, the system will log errors like JFS_LOG_WAIT or JFS_LOG_WRAP.

First try to reduce the filesystem activity. If that's not possible, this is the way to extend the JFS log:

  • Determine which log device to increase. This can be determined by its Device Major/Minor Number in the error log:
    # errpt -a
    An example output follows:
    Device Major/Minor Number
    000A   0003
    The preceding numbers are hexadecimal numbers and must be converted to decimal values. In this exmpale, hexadecial 000A 0003 equals to decimal numbers 10 and 3.
  • Determine which device corresponds with these Device Major/Minor Numbers:
    # ls -al /dev | grep "10, 3"
    If the output from the preceding command reveals that the log device the needs to be enlarged is /dev/hd8 (the default JFS log device for rootvg), then special actions are needed. See further on.
  • Increase the size of /dev/hd8:
    extendlv hd8 1
  • If the jfslog device is /dev/hd8, then boot the machine into Service Mode and access the root volume group and start a shell. If the jfslog is a user created jfslog, then unmount all filesystems that use the jfslog in question (use mount to show the jfslog used for each filesystem).
  • Format the jfslog:
    # logform [jsflog device]
    For example:
    logform /dev/hd8
  • If the jfslog device is /dev/hd8, then reboot the system:
    # sync; sync; sync; reboot
    If the jfslog is a user created jfslog, then mount all filesystems again after the logform completed.

If you found this useful, here's more on the same topic(s) in our blog:

UNIX Health Check delivers software to scan Linux and AIX systems for potential issues. Run our software on your system, and receive a report in just a few minutes. UNIX Health Check is an automated check list. It will report on perfomance, capacity, stability and security issues. It will alert on configurations that can be improved per best practices, or items that should be improved per audit guidelines. A report will be generated in the format you wish, and the report includes the issues discovered and information on how to solve the issues as well.

Interested in learning more?